Adhesives, such as hot melt adhesives, typically exist as entirely solid materials which do not contain or require any solvents. They are solid materials at ambient room temperature, but can be converted to a liquid or fluid state by the application of heat, in which state they may be applied to a substrate. On cooling, the adhesive regains its solid form and gains its cohesive strength. In this regard, hot melt adhesives differ from other types of adhesives, such as water-based adhesives, which achieve the solid state by evaporation, removal of solvents, polymerization, or other means. Hot melt adhesives may be formulated to be relatively hard and free of tack or, in contrast, to be pressure sensitive, i.e., relatively soft and tacky at room temperature.
These adhesives are particularly useful in the manufacture of a variety of industrial or consumer goods where bonding of various substrates is necessary, such as labels for packages, tapes of all types, end of line case and carton assembly and closure adhesives, non-woven adhesives, wood adhesives, book-binding adhesives, etc. Other applications include wax modification and traffic stripping. An advantage of hot melt adhesives is the absence of a liquid carrier, as would be the case for water-based or solvent-based adhesives, which requires a drying step during application of the adhesive. Suitable hot melt adhesives possess the appropriate bond strength to adhere the substrates involved, and also demonstrate adequate flexibility, no staining or bleed through of the substrate, suitable viscosity and open time to function on a variety of substrates, acceptable stability under storage conditions, and acceptable thermal stability under normal application temperature.
Hot melt adhesive compositions typically employ tackifying resins having softening points of at least 80° C. C5 diolefins such as 1,3-pentadiene, commonly known as piperylene, are the basic feed stock for the production of cationically polymerized tackifying resins. Piperylene is produced as a by-product of the steam cracking process whereby petroleum liquids are processed for the primary purpose of production of ethylene. Other olefins and diolefins such as 2-methyl-1-butene, 2-methyl-2-butene, and dicyclopentadiene are also produced. Tackifying resins prepared from C5 olefins and diolefins are known in the industry as “aliphatic” resins while those prepared from C5 olefins and diolefins along with one or more vinyl aromatic monomers, e.g., styrene and alpha-methyl styrene, are known as “aromatic modified” resins.
Due to its increased availability, low-cost gas is displacing liquids as feed stock in the steam cracking process for the production of ethylene. The result is that lower amounts of C5 diolefins are being produced leading to a shortage of this monomer for the production of tackifying resins. There is therefore a need for alternative monomers for the augmentation or even complete displacement of current petroleum-based diolefins for the production of tackifying resins that are cost-effective and readily available. The alternative monomers should preferably produce a resin having low odor and initial color and have compatibility with the adhesive resins commonly used in the formulation of hot melt and pressure sensitive adhesive compositions among other desirable properties.